Add Class.constructor tests

Squashed commits from https://github.com/xwpco/wordpress-develop/pull/44
qunit/index.html: added script tags for new unit tests
Added a return for readability
Removed extra tabs and returns
added space at end
removed extra tabs in qunit/index.html
Added space for readability
QUnit tests for section model
QUnit tests for panel model
moved closing parentheses
3 private functions moved into api.utils namespace
Unit tests for utility functions: customize-controls-utils.js
qunit tests for bubbleChildValueChanges
QUnit tests for bubbleChildValueChanges when two values are bound
bubbleChildValueChanges: added declarations
api.utils.getRootOfCustomizer() instead of separate uses of
QUnit test for getRootOfCustomizer
removed extra space
QUnit tests for wp.customize.ensure
customize-base.js: first tests for Value class